Corrosion inhibition for flowing steam and condensate lines



United States Patent 3,203,904 CORROSION INHIBITION FOR FLOWING STEAMAND CONDENSATE LINES James Kenneth Brown, Huntingdon Valley, Pa.,assignor to Betz Laboratories, Inc., Philadelphia, Pa., a corporation ofPennsylvania No Drawing. Filed Sept. 24, 1962, Ser. No. 225,828

8 Claims. (Cl. 252392) The present invention relates to processes andcompositions for controlling corrosion in flowing steam and condensatelines and particularly for avoiding or reducing the extent ofdegradation in long straight chain amines.

For some years long straight chain filming amines (U.S. Patent2,460,259) have been used to inhibit corrosion in condensate returnlines, steam lines, dryers, and other post boiler equipment, all ofwhich use flowing water or steam. Excellent inhibition of corrosion hasbeen attained by these materials, but in many cases the amine hasdegraded to a reddish-brown sludge which tends to deposit in the linesand therefore a great deal of maintenance is required to keep the linesfree.

The purpose of the invention is to provide an improved corrosioninhibitor for flowing steam and condensate lines, which will minimizethe tendency to degrade of the long straight chain amines now in use.

An extensive research program has been carried out to determine thetendency of various long straight chain amines to degrade. Table Iindicates some of the results obtained in this connection. Twenty gramsof each amine to be tested was placed in an oven maintained at 400degrees F. for hours. At the end of this period of test the separatesamples were removed from the oven. The appearance of the samples wasnoted and an infrared spectrogram was run on each sample. The band atabout 6.1 microns in the spectrogram is normally present in undegradedamines of this character only in trace amounts. The same is true ofundegraded amine-adducts.

By comparing the absorbance of the 6.1 band to the absorbance of the CHgroups at 6.8 microns, a relationship for undegraded amines wasestablished.

After heating, the absorbance at 6.1 microns was again measured andcompared to the absorbance of the CH band. This comparison of resultsbefore and after heating serves as a measure of the degradation.

Thus Table I shows for each amine tested a figure for this absorbanceratio before heating, another figure for the ratio after heating, and adifference corresponding to the amount of degradation.

The exact mechanism of the degradation process is not known to me, butit is commonly believed by authorities in this field to be an oxidationreaction which centers on the amine group. Based on evidence found inour own laboratory, however, it appears that reduction is the basicreaction. This is confirmed by the fact that the degraded amine has anabsorption band in the infrared absorption spectrum where the aldehydegroup is known to absorb.

When the amines referred to in Table I were tested for degradationtendencies by the measurement of the ratio of amide to CH as aboveexplained, it was noted that the amount of amine which degraded appearsto increase Patented Aug. 31, 1965 ice as the amine type varies fromprimary amine in Experiment 1 to secondary amine in Experiments 2 and 3and to tertiary amine in Experiments 4 and 5.

It is, therefore, very surprising to find that the formation of tertiaryamine by alkyloxylation in accordance with the present invention greatlyincreases the resistance to degradation rather than reducing it as withordinary tertiary amines.

Table I shows that the degradation of ethyloxylated or propyloxylatedamines was considerably less than that of other tertiary amines and wasmarkedly less than that of primary or secondary amines.

This behavior was observed with carbon chain lengths of from 8 to 22carbon atoms, and included both saturated and unsaturated amines.

The structural formula of the et-hyloxylated amines is shown below:

where:

R is a straight carbon chain from 8 to 22 carbon atoms long x is aninteger from 1 to 25 y is an integer from 1 to 25 The formula for thepropyloxylated amine is the same except for the substitution ofpropyloxylated groups (CH CH CH O) in place of the ethyloxyl (CH CH O).

Having found that alkyloxylation greatly decreases degradation, thealkyloxylated amines were tested to determine whether they are capableof inhibiting corrosion in a simulated condensate system. In the testthe effectiveness of the treatment to inhibit corrosion on low carbonsteel specimens of the character of A181 1010 was measured. A simulatedcondensate was prepared from demineralized water containing p.p.m. ofcarbon dioxide and less than 0.1 p.p.m. of oxygen. This water was heatedto degrees F. and was circulated over the four steel specimens in thesystem in series at a fiow rate of 0.35 foot per second. Weight lossessustained by the specimens when exposed to the condensate water bothuntreated and treated by the amines was the basis for evaluating thecorrosion inhibition.

The percentage protection was calculated by subtracting from the weightloss of the control the Weight loss of the treatment and dividing theresult by the control. Correct results based on the experiments areshown in Table II. It will be evident that Table II shows that somematerials which were satisfactory in the degradation test were notsatisfactory in the corrosion test.

First of all, all of the materials condensed with ethylene oxide whichhad more than 10 moles of ethylene oxide per mole of amine wereunsatisfactory from the standpoint of corrosion, in fact, they wereworse than the controls. It is therefore necessary to limit to 10 molesor less of ethylene oxide per mole of amine in order to obtain a productuseful from the standpoint of preventing corrosion.-

Furthermore, it was found that the condensate with propylene oxide inany concentration at all over the range tested promoted corrosion ratherthan helped corrosion protection, so that propylene oxide condensate iscounterindicated.

It was furthermore found as, for example, in Table II, Experiment 13,that the presence of double bonds does not affect the power to inhibitcorrosion to any appreciable extent as compared with the saturatedstraight chain long chain amines. In this Experiment 13 over 60% of theamine contains one or two double bonds, but this does not seriouslyaffect the corrosion protection.

Table II, Experiment 12, shows that short carbon chain amines containing8 to 14 carbon atoms in the carbon chain when condensed with only 2moles of ethylene oxide make the corrosion worse rather than better, andtherefore are counterindicated. Accordingly, the lower limit of theamine chain length has been placed at 16 carbon atoms.

All of these tests are short time tests and a concentration of 20 p.p.m.of active ingredient was used in such accelerated tests. As a practicalmatter, however, this concentration would normally be very expensive andusually a concentration in the range of 0.1 to p.p.m. is employed. Thereason for using the high concentration of 20 p.p.m. in the tests was toobtain representative results in the comparatively short time of 20hours. Since the treatment is one in which a protective film is carriedby the flowing stream of the condensate water or steam, and thusdeposited on the surface to be protected, it is only necessary to usesufficient treatment to gradually lay such a film. In actual practice,therefore, relatively low concentrations within the range specified arecommonly used. There are also factors in actual practice such as theamount of surface to be covered and the possibility of recycling theamine by using return condensate as feed which may vary the minimum feedconcentration to produce satisfactory protection. A feed concentrationof 0.84 p.p.m. of octadecylamine condensed with 2 moles of ethyleneoxide has proved to be very satisfactory in plant application, and basedupon my experiments 0.1 p.p.m. is the lowest (as found) reachingconcentration which brings reasonable protection under optimumconditions.

Experiments have been carried out to determine the degradation resistantproperties and the corrosion inhibitory properties of these materialsunder actual operating conditions. octadecylamine condensed with 2 molesof ethylene oxide was fed into an industrial plant condensate system asa dilute emulsified solution at the rate of 0.84 p.p.m. based on thesteam produced. In prior use of octadecylamine at this plant severedegradation of the amine in the condensate system had occurred. In thecase, however, of the amine ethylene oxide product as referred to above,the amount of old degradation products formed in the return line systemgradually decreased until the problem virtually disappeared. Thisvarified the findings obtained in the laboratory.

The corrosion protection continued to be of the same high order as thatobtained by octadecylamine alone.

METHOD OF FEED The primary straight long chain amines are hard waxysolids and they are diificult to emulsify in water for feeding purposes.The ethylene oxide products above re ferred to on the other hand areeasily prepared by the addition of any one of a number of well knownemulsifiers.

One of the most common of these is an ethoxylated quaternary ammoniumchloride salt as set forth below:

Formula I where R is a residue of a fatty acid having a carbon chainlength of 10 to 29 and preferably 10 to 24 inclusive, most desirably 10to 18 inclusive, such as a cocoanut acid residue containing C C and Cmixed fatty acid residues or an oleyl residue or a stearyl residue, andx and y total the mol ratio of polyoxyethylene to R in the molecule andinvolve a mol ratio of total polyoxyethylene to R of between 521 and15: 1. R can be saturated or can contain one double bond in the carbonchain.

These materials are commonly referred to as Ethoquads, and aredesignated by an initial letter or number, a slant line and a finalnumber such as Ethoquad 18/25. The initial letter or number designatesthe aliphatic group or groups which compose R as follows:

C :cocoanut acids residue, consisting of C C and C mixed 0=oleyl residue18=stearyl residue The number to the right of the slant line is thetotal of x+y10 so that Ethoquad 18/ 25 is of the stearyl series and hasa mol ratio of C H O to R of 15: 1.

Typical examples of the Ethoquads are as follows:

Ethoquad C/25 Ethoquad O/ 15 Ethoquad O/ 25 Ethoquad 18/ 15 Ethoquad18/25 It is preferred to use Ethoquad 18/25 in emulsifying the productsof the present invention. The emulsifier can be used in concentrationsfrom 5 to 20% on the dry weight of the amine and is preferably used in aconcentration of about 10% on the dry weight of the amine.

SUMMARY It will be evident that the present invention offers theadvantage of preventing degradation of the amine while permittingeffective corrosion protection in a flowing steam or condensate line,where the amine straight carbon chain has a length of from 16 to 22carbons atoms and is condensed with 1 to 10 moles inclusive of ethyleneoxide. The amine should be used in a quantity sufficient to coat theinterior of the line and preferably in a range between 0.1 and 20 p.p.m.and most desirably in a range between 0.1 and 10 p.p.m.

As shown by Table II, Experiments 6, 7 and 8, the protection is higherwith a concentration of ethylene oxide of 1 to 4 moles per mole ofamine, is slightly lower with a concentration of 5 moles per mole ofamine and the protection is not as good where the concentration is 10moles of ethylene oxide per mole of amine. Good amines to use areoctadecylamine and docosylamine, and preferably in the range of 1 to 4moles of ethylene oxide although .permissibly in the range from 1 to 10miles of ethylene oxide per mole of amine. Effective corrosionprotection may be obtained using docosylamine conthough permissibly inthe range from 1 to 10 moles of densed with 10 moles of ethylene oxide,or docosylamine condensed with 5 moles of ethylene oxide or docosylaminecondensed with 2 moles of ethylene oxide.

It will be evident that the water systems referred to in connection withthe present invention as flowing water systems will typically includesuch things as condensate return lines, steam lines, dryers and 'otherpost boiler equipment of this character which will typically have metalsurfaces of steel or of copper base alloys which must be protectedagainst corrosion.

In view of my invention and disclosure, variations and modifications tomeet individual whim or particular need will doubtless become evident toothers skilled in the art, to obtain all or part of the benefits of myinvention without copying the process and composition shown, and I,

therefore, claim all such insofar as they fall within the reasonablespirit and scope of my claims.

6 4. A process of claim 1, in which the amine is octadecylaminecondensed with 2 moles of ethylene oxide Table I.-Degradatin tests ofamines Absorbance at 6.1 Microns- N o. Amine Before After Amount heatingheating deg.

1 Oct y 0.139 0. 230 0. 091 2 Secondary Hydrogenated Tallow Amine 0. 0960.122 0. 026 3- Secondary Tallow Amine. 0. 141 0. 222 0. 081 4- Tertiarymethyl dihydrogenated tallow amine 0.118 0. 303 0.185 5. Tertiarydimethyl octadecylamine. O. 413 0. 671 0.258 6. Octadecylamine condensedwith 2 moles ethylene oxide adduct- 0.041 0. 043 0. 002 7.Octadeeylamine condensed with 5 moles ethylene oxide adduct- 0. 090 0.093 0.003 8- Octadecylamine condensed with moles ethylene oxide adduet-0. 173 0.174 0.001 9 Octadecylamine condensed with 50 moles ethyleneoxide adduct- 0. 054 0. 043 0. 011 10..-. Hydrogenated tallow aminecondensed with 2 moles propylene oxide adduet. 0.038 0. 040 0. 00211.-.. Hydrogenated tallow amine condensed with moles propylene oxideadduct- 0. 075 0. 135 0. 060 12.... Mixed straight chain primary aminescondensed with 5 moles ethylene oxide 0.178 0. 192 0. 014

per mole amine. 13.-.. Mixed straight chain primary amines condensedwith 15 moles ethylene oxide 0. 222 0.232 0.010

per mole amine. 14- Mixed straight chain primary amines condensed withmoles ethylene oxide 0. 175 0. 165 -0. 010

per mole amine." 15.-.. Mixed straight chain amines, some chainscontaining double bonds condensed 0.107 0.115 0. 008

with two moles of ethylene oxide per mole amine. 16.-.. Same as 15 butcondensed with 5 moles ethylene oxide per mole of amine 0. 210 0. 216 0.006 Same as 15 but condensed with 15 moles ethylene oxide per mole ofamine 0. 099 0. 100 0.001 18.... Mixed straight chain amines 0. 024 0.440 0. 416 19.-.- Mixed straight chain amines as in 18 condensed with 2moles ethylene oxide 0. 036 0.066 0.030

per mole of amine.

1 The amount degraded is the difference in absorbance units between theintensity of the absorbance, at 6.1 microns, before and after heating.It is therefore a measure of the susceptibility to degradation by heatof the compound measured. The intensity of the absorbance of the carbonto hydrogen bond at 6.8 microns was used as a measure of the thicknessof the amine sample in the infrared beam. The absorbance of the amideband at about 6.1 microns was calculated on the basis of a 1.0absorbance for the 6.8 micron carbon to hydrogen band.

1 Chain length varied from 8 to 14 with 12 predominating.

3 Chain lengths were 16 and 18 carbon atoms long.

4 Chain lengths were 16 to 22 carbon atoms long.

Table Il.-C0rr0sion protection by amines in condensate No. Treatment MgsPercent loss protection None 43. 4 0. 00 0ctadecylamine. 4. 6 89. 6Secondary tallow a Could not be fed Tertiary methyl di(Hydrogenatedtallow) amine. 108.0 151 Tertiary dimethyl o'ctadeeylamine 41. 4 4. 6Octadecylamine condensed with 2 moles ethylene 0x1 e- 5. 0 88. 5Octadeeylamine condensed with 5 moles ethylene oxide- 12. 2 72. 0Octadecylamine condensed with 10 moles ethylene oxide 30. 2 30. 5Octadecylamine condensed with 50 moles ethylene oxide 61.3 41. 4 10.-.Hydrogenated tallow amine condensed with 2 moles propylene oxide adduct.63.2 46 11 Hydrogenated tallow amine condensed with 15 moles propyleneoxide adduct 99. 9 -133 12..-- Mixed straight chain primary aminescondensed with two moles ethylene 55. 7 28. 4

oxide per mole amine 13"... Mixed straight chain amines, some chainscontaining double bonds condensed 9. 7 78 with two moles ethylene oxideper mole amine. 14... Same as 13 but condensed with 50 moles ethyleneoxide per mole of am ne--. 51. 6 -19 15 Mixed straight chain aminescondensed with two moles ethylene oxide per 5. 5 87. 5

mole of amine.

1 Chain length varied from 8 to 14 carbon atoms with the 12 carbon atomschain length predominating. 2 Chain lengths contained 16 and 18 carbonatoms. a Chain lengths varied from 16 to 22 carbon atoms.

and the quantity of said amine in said water system does not exceed 10p.p.m.

Having thus described my invention what I claim as new and desire tosecure by Letters Patent is:

1. A process of preventing corrosion in steam and condensate linesforming a flowing Water system, which comprises maintaining in theflowing stream of such a Water system as effectively the only corrosioninhibitor a dispersion of from 0.1 to 20 p.p.m. of a primary straightchain amine of 16 to 22 carbon atoms chain length condensed with 1 to 10moles of ethylene oxide, the quantity of corrosion inhibitor beingsuflicient to form a protective film on the inside of said water system.

2. A process of claim 1, in which the amine is octadecylamine condensedwith 10 moles of ethylene oxide and the quantity of said amine in thewater system does not exceed 10 p.p.m.

3. A process of claim 1, in which the amine is oct-adecylamine condensedwith 5 moles of ethylene oxide and the quantity of said amine in saidwater system does not exceed 10 p.p.m.

5. A process of claim 1, in which the amine is docosylamine condensedwith 10 moles of ethylene oxide and the quantity of said amine in saidwater system does not exceed 10 p.p.m.

6. A process of claim 1, in which the amine is docosylamine condensedwith 5 moles of ethylene oxide, and the quantity of said amine in saidwater system does not exceed 10 p.p.m.

7. A process of claim 1, in which the amine is docosylamine condensedwith 2 moles of ethylene oxide and the quantity of said amine in saidwater system does not exceed 10 ppm.

8. A process of claim 1, in which the amine constitutes mixed primarysaturated straight carbon chain amines and the quantity of said amine insaid water system does not exceed 10 p.p.m.

(References on following page) 7 References Cited by the Examiner2,894,905 7/59 UNITED STATES PATENTS 2%; 2,564,758 8/51 Haggard 2528.553 113 113 12 3 2,745,809 5/56 Cardwell et a1. 2528. 55 5 2,759,975 8/56ChiddiX et a1 260567.6

8 Bernard 252-390 XR Denman 252-390 XR Kahler et a1. 252392 XR Marsh eta1. 252390 XR JULIUS GREENWALD, Primary Examiner.

1. A PROCESS OF PREVENTING CORROSION IN STREAM AND CONDENSATE LINESFORMING A FLOWING WATER SYSTEM, WHICH COMPRISES MAINTAINING IN THEFLOWING STREAM OF SUCH A WATER SYSTEM AS EFFECTIVELY THE ONLY CORROSIONINHIBITOR A DISPERSION OF FROM 0.1 TO 20 P.P.M. OF A PRIMARY STRAIGHTCHAIN AMINE OF 16 TO 22 CARBON ATOMS CHAIN LENGTH CONDENSED WITH 1 TO 10MOLES OF ETHYLENE OXIDE, THE QUANTITY OF CORROSION INHIBITOR BEINGSUFFICIENT TO FORM A PROTECTIVE FILM ON THE INSIDE OF SAID WATER SYSTEM.